The functions in this section look at or change the text of one or more strings.
index(in, find)
This searches the string in for the first occurrence of the string find, and returns the position in characters where that occurrence begins in the string in. For example:
awk 'BEGIN { print index("peanut", "an") }'
prints `3'. If find is not found, index returns 0. (Remember that string indices in awk start at 1.)
length(string)
This gives you the number of characters in string. If string is a number, the length of the digit string representing that number is returned. For example, length("abcde") is 5. By contrast, length(15 * 35) works out to 3. How? Well, 15 * 35 = 525, and 525 is then converted to the string `"525"', which has three characters. If no argument is supplied, length returns the length of $0. In older versions of awk, you could call the length function without any parentheses. Doing so is marked as "deprecated" in the POSIX standard. This means that while you can do this in your programs, it is a feature that can eventually be removed from a future version of the standard. Therefore, for maximal portability of your awk programs you should always supply the parentheses.
match(string, regexp)
The match function searches the string, string, for the longest, leftmost substring matched by the regular expression, regexp. It returns the character position, or index, of where that substring begins (1, if it starts at the beginning of string). If no match if found, it returns 0. The match function sets the built-in variable RSTART to the index. It also sets the built-in variable RLENGTH to the length in characters of the matched substring. If no match is found, RSTART is set to 0, and RLENGTH to -1. For example:
awk '{
if ($1 == "FIND")
regex = $2
else {
where = match($0, regex)
if (where)
print "Match of", regex, "found at", where, "in", $0
}
}'
This program looks for lines that match the regular expression stored in the variable regex. This regular expression can be changed. If the first word on a line is `FIND', regex is changed to be the second word on that line. Therefore, given:
FIND fo*bar
My program was a foobar
But none of it would doobar
FIND Melvin
JF+KM
This line is property of The Reality Engineering Co.
This file created by Melvin.
awk prints:
Match of fo*bar found at 18 in My program was a foobar
Match of Melvin found at 26 in This file created by Melvin.
split(string, array, fieldsep)
This divides string into pieces separated by fieldsep, and stores the pieces in array. The first piece is stored in array[1], the second piece in array[2], and so forth. The string value of the third argument, fieldsep, is a regexp describing where to split string (much as FS can be a regexp describing where to split input records). If the fieldsep is omitted, the value of FS is used. split returns the number of elements created. The split function, then, splits strings into pieces in a manner similar to the way input lines are split into fields. For example:
split("auto-da-fe", a, "-")
splits the string `auto-da-fe' into three fields using `-' as the separator. It sets the contents of the array a as follows:
a[1] = "auto"
a[2] = "da"
a[3] = "fe"
The value returned by this call to split is 3. As with input field-splitting, when the value of fieldsep is " ", leading and trailing whitespace is ignored, and the elements are separated by runs of whitespace.
The sub function alters the value of target. It searches this value, which should be a string, for the leftmost substring matched by the regular expression, regexp, extending this match as far as possible. Then the entire string is changed by replacing the matched text with replacement. The modified string becomes the new value of target. This function is peculiar because target is not simply used to compute a value, and not just any expression will do: it must be a variable, field or array reference, so that sub can store a modified value there. If this argument is omitted, then the default is to use and alter $0. For example:
sets str to "wither, water, everywhere", by replacing the leftmost, longest occurrence of `at' with `ith'. The sub function returns the number of substitutions made (either one or zero). If the special character `&' appears in replacement, it stands for the precise substring that was matched by regexp. (If the regexp can match more than one string, then this precise substring may vary.) For example:
awk '{ sub(/candidate/, "& and his wife"); print }'
changes the first occurrence of `candidate' to `candidate and his wife' on each input line. Here is another example:
prints `dcaacbaaa'. This show how `&' can represent a non-constant string, and also illustrates the "leftmost, longest" rule. The effect of this special character (`&') can be turned off by putting a backslash before it in the string. As usual, to insert one backslash in the string, you must write two backslashes. Therefore, write `\\&' in a string constant to include a literal `&' in the replacement. For example, here is how to replace the first `|' on each line with an `&':
awk '{ sub(/\|/, "\\&"); print }'
Note: as mentioned above, the third argument to sub must be an lvalue. Some versions of awk allow the third argument to be an expression which is not an lvalue. In such a case, sub would still search for the pattern and return 0 or 1, but the result of the substitution (if any) would be thrown away because there is no place to put it. Such versions of awk accept expressions like this:
sub(/USA/, "United States", "the USA and Canada")
But that is considered erroneous in gawk.
gsub(regexp, replacement, target)
This is similar to the sub function, except gsub replaces all of the longest, leftmost, nonoverlapping matching substrings it can find. The `g' in gsub stands for "global," which means replace everywhere. For example:
replaces all occurrences of the string `Britain' with `United Kingdom' for all input records. The gsub function returns the number of substitutions made. If the variable to be searched and altered, target, is omitted, then the entire input record, $0, is used. As in sub, the characters `&' and `\' are special, and the third argument must be an lvalue.
substr(string, start, length)
This returns a length-character-long substring of string, starting at character number start. The first character of a string is character number one. For example, substr("washington", 5, 3) returns "ing". If length is not present, this function returns the whole suffix of string that begins at character number start. For example, substr("washington", 5) returns "ington". This is also the case if length is greater than the number of characters remaining in the string, counting from character number start.
tolower(string)
This returns a copy of string, with each upper-case character in the string replaced with its corresponding lower-case character. Nonalphabetic characters are left unchanged. For example, tolower("MiXeD cAsE 123") returns "mixed case 123".
toupper(string)
This returns a copy of string, with each lower-case character in the string replaced with its corresponding upper-case character. Nonalphabetic characters are left unchanged. For example, toupper("MiXeD cAsE 123") returns "MIXED CASE 123".
